Lecture 2+3 (GENETICS), EXAM 3 Flashcards
What is genetics?
What is a gene?
- Scientific study of gene and heredity, how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence
- Gene- a segment of DNA that contains instructions for building one or more molecules, i.e proteins
Gene:
* Unit of what?
* gene achieves their effects by what?
* Eukaryotes vs prokaryotes?
- Unit of heredity information that occupies a fixed position on a chromosome
- Genes achieve their effects by directing the synthesis of proteins
- Eukaryotes- genes are contained within the cell nucleus
- Prokaryotes (they lack a nucleus)- genes are contained in a single chromosome that is free floating in the cell cytoplasm – some bacteria have plasmids – extrachromosomal genetic elements with a small number of genes
Genome
- What a genome?
- Organisms entire genome is found where?
- Genome is housed where?
- Prokaryotic vs eukaryptic cells?
- DNA is stored in what?
- Humans have how many pairs of chromosomes?
- Two chromosomes in each pair contain what?
- Reproductive cells (egg/sperm)- have _ chromosomes
Rosalind Franklin:
* Performed what?
* Discovered what?
* Determined what?
- Performed X-ray diffraction studies to identify the 3-D structure
- Discovered that DNA is helical
- Determined that the molecule has a uniform diameter
James Watson & Francis Crick – 1953
* What did they find out?
* Proposed what?
* _ figure as he aged
- Genes carry what? What must happen?
- DNA encodes what? How?
- The message from DNA encodes what?
- Linear sequence of nucleotides in a gene spell out what?
DNA
- Another name for DNA?
- What does it carry?
- DNA shape?
- Deoxyribonucleic acid
- Carries genetic information for development and functioning of an organism
- Shape known as a double helix
What is dna composed of?
Composed of nucleotides
* 5-carbon sugar called deoxyribose
* Phosphate group (PO4)-> Attached to 5ʹ carbon of sugar
* Nitrogenous base: Adenine, thymine, cytosine, guanine
* Free hydroxyl group (—OH)-> Attached at the 3ʹ carbon of sugar
- 5-carbon sugar called what?
- Phosphate group attaches where?
- What are nitogenous bases?
- Where does the free hydroxyl group attach?
- Erwin Chargaff determined what?
- What is always equally proportional?
Erwin Chargaff determined :
* Amount of adenine = amount of thymine
* Amount of cytosine = amount of guanine
Always equal proportion: purines & pyrimidines
- How many base pairs make up the human genome?
- How many genes in human genome?
- What has their own set of genes? why?
- 3.2 billion base pairs make up the human genome
- BUT the marbled lungfish has about 133 billion of them in its genome!!
- Approximately 20,000-25,000 genes in the human genome
- 37 genes in the mitochondrial genome – mitochondria have their own set of genes because they are thought to have evolved from bacteria that were engulfed by eukaryotic cells some 1.5 billion years ago
- How long is your DNA if you uncoil it from one of your cells and place them end to end?
- How long would it be if you did this to all your cells?
- 6 feet (2 meters) of length if you uncoiled the DNA from one of your cells and placed them end to end.
- Do this for all your DNA and the resulting strand would be 67 billion miles long – approx. 150k trips around theMoon
- What is the percentage of DNA is the same between two people on earth? What about the variation?
- What also contributes?
- 99.6% is how identical DNA of two people on earth is. The 0.4% variation represents about 12 million base pairs which explains the differences between individuals.
- Our environment also contributes
98% of our genome is what? Explain
98% of our genome is noncoding DNA – DNA that doesn’t contain information to make proteins – this “junk” DNA has other jobs that we are still learning about
- What are chromosomes composed of?
- DNA of a single chromosome is what?
- Typical human chromosome is how long?
- Composed of chromatin – complex of DNA and protein
- DNA of a single chromosome is one long continuous double-stranded fiber
- Typical human chromosome is 140 million nucleotides long (280 books – 1000 pages – 500 words/page
Nucleosome:
* Complex of what?
* Promote and guide what?
* DNA duplex coiled around what?
* What are histones?
- Complex of DNA and histone proteins
- Promote and guide coiling of DNA
- DNA duplex coiled around 8 histone proteins every 200 nucleotides
- Histones are positively charged and strongly attracted to negatively charged phosphate groups of DNA
At each cell division, the cell must do what?
must copy its genome to pass it to both daughter cells.
The discovery of the structure of DNA also revealed what? Explain
The discovery of the structure of DNA also revealed the principle that makes this copying possible: because each strand of DNA contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand, each strand can act as a template, or mold, for the synthesis of a new complementary strand.
if we designate the two DNA strands as S and Sʹ:
* What is the S and S’ strand?
* How does it happen?
- In other words, if we designate the two DNA strands as S and Sʹ, strand S can serve as a template for making a new strand Sʹ, while strand Sʹ can serve as a template for making a new strand S.
- Thus, the genetic information in DNA can be accurately copied by the beautifully simple process in which strand S separates from strand Sʹ, and each separated strand then serves as a template for the production of a new complementary partner strand that is identical to its former partner.
Replication and Reproduction: Bacteria/Prokaryote
- Bacteria divide by what?
- What do they not have?
- Reproduction is what?
- Bacteria divide by binary fission
- No sexual life cycle
- Reproduction is clonal
Replication and Reproduction: Bacteria/Prokaryote
- What is replicated?
- Replication begins where and proceeds how?
- New chromosomes are what?
- What is formed?
- Single, circular bacterial chromosome is replicated
- Replication begins at the origin of replication and proceeds in two directions to site of termination
- New chromosomes are partitioned to opposite ends of the cell
- Septum forms to divide the cell into 2 cells
Reproduction and Replication: Eukaryotes
- What is mitosis?
- Prior to onset of mitosis the chromosomes have what?
- What do the cells do?
Mitosis – process by which a cell replicates its chromosomes and then segregates them producing two identical nuclei in preparation for cell division
* Prior to onset of mitosis the chromosomes have replicated
* The cells copy chromosomes and make sure the one copy goes to each daughter cell
Reproduction and Replication: Eukaryotes
What is meiosis?
Meiosis – cell division in sexually reproducing organisms that reduces the number of chromosomes in egg or sperm cells, “haploid”
Karyotype
- What is a karyotype? How is it arranged?
- Humans are what? Two complete sets of what? How many total chromosomes?
- Sex cells are what? One set of what? Which pair of chromosome is the sex chromosomes
- Particular array of chromosomes in an individual organism
* Arranged according to size, staining properties, location of centromere, etc. - Humans are diploid (2n)
* 2 complete sets of chromosomes
* 46 total chromosomes - Sex cells are haploid (n) – 1 set of chromosomes
* 23 in humans
Karyotype
Pair of chromosomes are what? Each one is what?
Pair of chromosomes are homologous
* Each one is a homologue
Who is Josef Kolreuter? What did he do?
Josef Kolreuter – 1760 – crossed tobacco strains to produce hybrids that differed from both parents
* Additional variation observed in 2nd generation offspring contradicts direct transmission
Who is T.A. Knight? What did he do/discovered?
T.A. Knight – 1823 – crossed 2 varieties of garden pea, Pisum sativa
* Crossed 2 true-breeding strains
* 1st generation resembled only 1 parent strain (were heterozygotes - were demonstrating dominance but did not realize it)
* 2nd generation resembled both (3 dominants:1 recessive)
Why did gregor mendel chose to study pea plants?
- Previous research showed that pea hybrids could be produced
- Many pea varieties were available
- Peas are small plants and easy to grow
- Peas can self-fertilize or be cross-fertilized
Mendel’s experimental method is usually 3 stages, explain them
- Produce true-breeding strains for each trait he was studying
- Cross-fertilize true-breeding strains having alternate forms of a trait
* Also perform reciprocal crosses - Allow the hybrid offspring to self-fertilize for several generations and count the number of offspring showing each form of the trait
- What is a Monohybrid cross?
- Mendel produced what? How many traits? Each trait had how many variants?
- Cross to study only 2 variations of a single trait
- Mendel produced true-breeding pea strains for 7 different traits-> Each trait had 2 variants
Homozygous vs heterozygous?
- homozygous: An allele pair that is the same
- heterozygous: An allele pair that is different
F1 generation:
* What is it?
* Offspring produced by what?
* For every trait Mendel studied, all F1 plants resembled what? What is trait referred to? Alternative trait was what?
* What was not produced?
- First filial generation
- Offspring produced by crossing 2 true-breeding strains
- For every trait Mendel studied, all F1 plants resembled only 1 parent
* Referred to this trait as dominant
* Alternative trait was recessive - No plants with characteristics intermediate between the 2 parents were produced
F2 generation:
* What is it?
* Offspring resulting from what?
* What has reappeared?
* What is the ratio?
- Second filial generation
- Offspring resulting from the self-fertilization of F1 plants
- Although hidden in the F1 generation, the recessive trait had reappeared among some F2 individuals
- Counted proportions of traits->Always found about 3:1 ratio
3:1 is actually what? Explain this with the dominant and recessive form
F2 plants
* 3⁄4 plants with the dominant form
* 1⁄4 plants with the recessive form
* The dominant to recessive ratio was 3:1
Mendel discovered the ratio 3:1 is actually what?
- 1 true-breeding dominant plant
- 2 not-true-breeding dominant plants
- 1 true-breeding recessive plant
For mendel:
* His plants did not show what? Each trait was what?
* For each pair, what were the traits?
* Pairs of alternative traits examined were what?
* Alternative traits were expressed in the F2 generation in the ratio of what?
- His plants did not show intermediate traits ->Each trait is intact, discrete
- For each pair, one trait was dominant, the other recessive
- Pairs of alternative traits examined were segregated among the progeny of a particular cross
- Alternative traits were expressed in the F2 generation in the ratio of 3⁄4 dominant to 1⁄4 recessive
- What is a phenotype? What is a genotype?
- What is recessive and dominant?
- Phenotype: physical traits of an individual
- Genotype: genetic composition of an individual; describes alleles
- Recessive: the phenotype of an allele is seen only when homozygous - aa
- Dominant: the phenotype is seen when homozygous or heterozygous – AA or Aa
Under genotype, what is homozygous and heterozygous?
- Homozygous: homozygote carries two copies of the same allele - AA or aa
- Heterozygous: heterozygote carries two different alleles for a gene - Aa
What are punnett squares?
table that predicts possible outcomes of a cross (mating between two parents)
Consider a cross between two cystic fibrosis carriers
* “F”=normal allele;“f”=recessive disease allele
* The cross would be Ff xFf
* What offspring could result?
- 1 Homozygous normal
- 2 Heterozygous carrier
- 1 Homozygous diseased
What is incomplete dominance? Give an example
Incomplete dominance: a heterozygote expresses an intermediate, “blended” phenotype
* RR = red flowers
* rr = white flowers
* Rr = pink flower
What is codominance? What is an example?
Codominance: the heterozygoteʼs phenotype is a combination of two fully expressed traits
* R1R1 = red coat color in cattle
* R2R2 = white coat color in cattle
* R1R2 = roan coat color (red and white)
What are polygenic traits and pleiotropy?
- Polygenic traits: multiple genes converge to result in a single phenotype
- Pleiotropy: a phenomenon in which a single gene contributes to multiple phenotypic traits – the individual allele has more than one effect on the phenotype
Pleiotropy:
* What is are three examples?
- Example: mutation in any one of the genes that affect tyrosine synthesis, would affect multiple body systems (needed for protein synthesis, precursor for several neurotransmitter, hormone thyroxine)
- Marfan syndrome
- Phenylketonuria (most widely cited example of pleiotropy) – caused by a deficiency of the enzyme phenylalanine hydroxylase, which is necessary to convert the essential amino acid phenylalanine to tyrosine – defect results in mental retardation, eczema, pigment defects
Polygenic inheritance:
* Occurs when?
* The phenotype is what?
* These traits show what? Give example and what does the histogram show?
- Occurs when multiple genes are involved in controlling the phenotype of a trait
- The phenotype is an accumulation of contributions by multiple genes
- These traits show continuous variation and are referred to as quantitative traits
* For example – human height
* Histogram shows normal distribution
Multiple alleles:
* What is it?
* What is an example?
* Each individual can only have what?
* Number of alleles possible for any gene is what?
- May be more than 2 alleles for a gene in a population
- ABO blood types in humans->3 alleles
- Each individual can only have 2 alleles
- Number of alleles possible for any gene is constrained, but usually more than two alleles exist for any gene in an outbreeding population
Human ABO blood group
- Who discovered ABO blood group?
- The ABO blood group antigens are encoded by what?
- Off spring receives one of the three alleles from each parent, giving rise to what?
- Karl Landsteiner has been credited for the discovery of ABO blood group system in 1900
- The ABO blood group antigens are encoded by one genetic locus, which has three alternatives (allelic) forms, A, B, and O
- Off spring receives one of the three alleles from each parent, giving rise to 6 possible genotypes and 4 possible blood types (phenotypes)
Human ABO blood group
The system demonstrates both
* What is multiple alleles
* What is codominance?
Multiple alleles
* 3 alleles of the I gene (IA, IB, and i)
Codominance
* IA and IB are dominant to i but codominant to each other
Extensions of Mendelian Genetics
ABO blood group has three alleles of one gene, explain
*IA is dominant to i.
*IB is dominant to i.
*IA and IB are co-dominant.
* Individual genotypes will show two of these alleles.
What are multiple alleles?
more than two alleles of a gene are possible
ABO blood system - phenotypes has what on their surface?
- Type A has sugar A on the surface of blood cells.
- Type B has sugar B on the surface of blood cells.
- Type O has no sugars on the surface of blood cells.
- Type AB has sugar A and sugar B on the surface of blood cells.
What is blood type analysis?
can be used to exclude potential parents
- AB parent can never have what type of child?
- Two Rh– parents can never have what type of child?
- If you have certain sugars on your blood cell, then you have what?
- Antibodies cause what?
- AB parent can never have an O child.
- Two Rh– parents can never have a Rh+ child.
- If you have certain sugars on your blood cell: A, B, AB – then you have antibodies to opposite sugars.
- Antibodies cause reactions to blood cells if incompatible
Sex Chromosomes
- human genome organized into what?
- How many pairs of autosomes and sex chromosomes?
human genome organized into 23 pairs of chromosomes
* 22 pairs of autosomes
* 1 pair of sex chromosomes
- X and Y chromosome determine what?
- What do females and males inherit?
X and Y chromosome determine the biological sex of an individual
* Females inherit an X chromosome from the father for a XX genotype
* Males inherit a Y chromosome from the father for a XY genotype
- Mothers’ only pass on what?
- What is the biological default?
- The presence of a Y chromosome is critical because why?
- Mothers’ only pass on X chromosomes
- The biological default is female development.
- The presence of a Y chromosome is critical because it contains the genes necessary to override the default
How many genes are in X chromosomes and Y chromosomes
X chromosome: 900-1600 genes
Y chromosome: 70-200
X Chromosome:
* Has about how many protein coding genes?
* For most genes on the X chromosome only needs what?
* Females have two X chromosomes and therefore two copies of every X-linked gene so one copy is what?
* Males have only one X chromosome and therefore only one copy is what?
- Has about 900 protein coding genes
- For most genes on the X chromosome only one copy is required
- Females have two X chromosomes and therefore two copies of every X-linked gene so one copy is randomly inactivated or turned off, however the second can be used if the first has abnormalities
- Males have only one X chromosome and therefore only one copy is expressed
The Y Chromosome:
* Codes for only what?
* The Y chromosome’s role in sex determination is clear, but research has shown what?
* The SRY genes on the Y chromosome produces what?
- Codes for only 100 proteins
- The Y chromosome’s role in sex determination is clear, but research has shown that the Y chromosome it is undergoing rapid evolutionary deterioration
- The SRY genes on the Y chromosome produces a protein that activates other genes that cause the embryo to develop sex characteristics of a male
Many generations ago the Y chromosome was what? What about now?
- Many generations ago the Y chromosome was large and contained as many genes as the X chromosome
- Now it is a fraction of the its past size and contains fewer than 80 functional genes
- All individuals who have a Y chromosome are related through what?
- Many health conditions are thought to be related to what?
- All individuals who have a Y chromosome are related through a single Y-bearing ancestor who likely lived around 300,000 years ago
- Many health conditions are thought to be related to changes in genes on the Y chromosome - currently an active area of research!
What is XXY?
Klinefelter’s syndrome – mild or severe symptoms
* result from low testosterone. Not detected in early childhood, puberty brings out disruptions (smaller testes, penis, infertility, breast growth, reduced muscle tone, weaker bones)
Conditions where you have more than two sex chromosomes in your cells
What is XYY?
Jacobs syndrome – increased risk for asthma, seizure disorders, autism, learning disabilities, behavioral problems
Conditions where you have more than two sex chromosomes in your cells
What is XXX?
Triple X Syndrome – many have no symptoms, can have fertility issues, be tall, wide-spaced eyes, curved or bent little fingers, poor muscle tone
Conditions where you have more than two sex chromosomes in your cells
What is X?
Turner syndrome – when patient has one missing, either partially or completely, X chromosome
Conditions where you have one sex chromosome
X – Turner syndrome:
* What are the symptoms?
* Affects how many?
* What is monosomy X
* What is mosaic tuner syndrome?
* What is inherited turner syndrome?
- Symptoms: short stature, ovary function, delayed puberty, amenorrhea (no menstruation)
- Affects 1 in 2,000-2,500 babies - most common sex chromosome-related condition
- Monosomy X – only one X chromosome, 45% of Turner’s syndrome
- Mosaic Tuner syndrome- makes up 30% - some of child’s cells have pair, other only have one
- Inherited Turner syndrome – biologic parent born with it and passes it on
What are Sex-linked genes?
X-Linked located on what?
* Males inherit X from who?
* Males are more likely to what? Why?
* Females are less likely to what? Why?
Y Linked located on what?
* Passes from father to who?
* What gene leads to the development of testes?
Sex-linked genes: genes located on the sex chromosomes
X-linked: located on the X chromosome
* Males inherit the X from their mother.
* Males are more likely to express X-linkage since they carry only one X chromosome
* Females are less likely to express X-linkage because must carry two defective X chromosomes
Y-linked: located on the Y chromosome
* Passes from father to sons
* SRY gene, which leads to the development of the testes
- Who does X-linked Recessive Alleles affect more?
- X-linked recessive alleles example?
Certain genetic diseases affect males to a greater degree than females
X-linked recessive alleles
* Red-green color blindness – person cannot distinguish shades of red and green, but their ability to see is normal
What is another x-linked recessive alleles?
Hemophilia-blood clotting disorder
Hemophilia-blood clotting disorder:
* What does it cause?
* What is located on the X chromosome?
* Males can only pass to who?
* Female carriers may not know what?
- Causes inability to clot, excessive bruising, fatigue, joint pain and swelling, anemia
- Gene for this clotting factor is on the X chromosome.
- Males can only pass to their daughters who can then pass to their sons
- Female carriers may not know they have the allele until a son becomes ill
- What is hemophilia A?
- Common or uncommon?
- Female carrier of the gene may show what?
- Hemophilia A is a disorder where the blood cannot clot properly due to a deficiency of Factor VIII (8).
- Accounts for most cases
- Female carrier of the gene may show some mild signs of easy bruising
Hemophilia B is a deficiency of what?
Factor IX
- What is hemophilia A? B?
- Which one ^ accounts for most causes?
- Female carrier of the gene may show some what?
- Hemophilia A is a disorder where the blood cannot clot properly due to a deficiency of Factor VIII (8).
- Hemophilia B is a deficiency of Factor IX
- Hemophilia A accounts for most cases
- Female carrier of the gene may show some mild signs of easy bruising
What is pedigree?
a chart that diagrams the inheritance of a trait or health conditions through generations of a family.
- A family tree shows what?
- What is commonly used symbols in pedigrees?
- Possession of the characteristic is shown by what? The absence is shown by what?
- a family tree; shows trait inheritance through several
generations - Circles (female) and squares (males) are commonly used symbols in pedigrees.
- Possession of the characteristic is shown by solid or blackened symbol, the absence is shown by an open or clear symbol
What type of pedigree?
Dominant
What type of pedigree?
What type of pedigrees
- Left: X-linked recessive
- Right: X-linked dominant
Hemophilia:
* What does it affect?
* Caused by what? Heterozygous females are what?
* Allele for hemophilia was introduced into what?
- Review: disease that affects a single protein in a cascade of proteins involved in the formation of blood clots
- Caused by an X-linked recessive allele->Heterozygous females are asymptomatic carriers
- Allele for hemophilia was introduced into a number of different European royal families by Queen Victoria of England
